Rein tensions and behaviour with five rein types in international-level vaulting horses.

Health and performance of vaulting horses cantering with reins might be affected by rein tensions. The primary aim of this present study was to measure rein and lunge line tensions in international-level vaulting horses with several types of reins adjusted in accordance with the requirements of the FEI Vaulting Rules and study the effect of reins types on it. The secondary aim was to evaluate behavioural signs of discomfort under the same conditions and study the effect of reins types on it. The relationship between tensions and behavioural signs of discomfort was then explored. Thirty-nine international-level vaulting horses took part in this study and tested side reins either with an elastic part, all elastic or without elastic, draw reins with an upper adjustment triangle and side reins fixed on the noseband. Tensions of the left and right reins and the lunge line were measured with sensors at a rate of 80 Hz for a canter of 1min30 on a 15-meter circle, without a vaulter, and behavioural analyses (on the locomotion, tail, head, mouth and ears movements) were performed using video filmed by a camera attached to the lunger's chest. Mixed models revealed that the Root mean square (RMS) of the tensions of the left and right reins, of the total, as well as the lunge line, were significantly influenced by rein type (p<0.001) in all cases). Total RMS tension ranged from 6.2 kg to 11.7 kg with a right RMS tension superior to left RMS (p < 0.001). When tension was high, mouth opening increased (p = 0.007). It was with draw reins that total tension (p < 0.05) and mouth openings were lower (p = 0.005), even if a high proportion of variance of these discomfort behaviours could be explained by the individual horse.